This invention is directed to a focused ion beam column particularly useful for scanning a small spot over a large field for the exposure of resist material. The column has the capability of exposing images smaller than 0.1 micrometer (micron) and has the capability of addressing a field of about 1 millimeter square at the target while maintaining the aberration limited spot size to less than about 1,000 .ANG..
Previous focused ion beam columns for the exposure of resist have required that the scanfields be restricted to very small dimensions because deflection associated aberrations would cause an increase in spot size to more than 125% of the axial spot size. This limited scanfield arises from a short working distance associated with the final lens. Therefore, there is a need for a focused ion beam column wherein a small spot size can be scanned over a large field.